lg 2234s no power at all

[vagos_89]

Re: lg 2234s no power at all

I tested the mosfet and is ok. I try a new one for sure but the problem remains.

I dont have any voltage on the transformer in secondary in any pin consequently i dont have voltage to the output connector.
In the primary of the transformer i have these DCV pin1 326V pin2(not connected) pin3 326V pin4 0V pin 5 0V.

The dc voltage between two legs of c807 is 3,1V

[budm]

Re: lg 2234s no power at all

"The dc voltage between two legs of c807 is 3,1V" That Voltage is way to low for the SMPS IC to run. You already test the rectifier diodes in the secondary side to make sure they are not bad.
The SMPS may be in the shutdown mode, or bad startup/running cap, bad SMPS IC.

[vagos_89]

Re: lg 2234s no power at all

"The dc voltage between two legs of c807 is 3,1V" That Voltage is way to low for the SMPS IC to run. You already test the rectifier diodes in the secondary side to make sure they are not bad.

Yes i test the rectifiers in secondary and are good. Also i replace and c807 but nothing.

The SMPS may be in the shutdown mode, or bad startup/running cap, bad SMPS IC.

Sorry but what do you mean "SMPS IC"? You mean the IC802 LD7522 on the bottom of the board?

[budm]

Re: lg 2234s no power at all

SMPS: SWITCHED MODE POWER SUPPLY.
"You mean the IC802 LD7522 on the bottom of the board?" Yes, please see the spec sheet attached so you can see the pin out and how it functions.

[vagos_89]

Re: lg 2234s no power at all

SMPS: SWITCHED MODE POWER SUPPLY.
"You mean the IC802 LD7522 on the bottom of the board?" Yes, please see the spec sheet attached so you can see the pin out and how it functions.

Thanks, i've already found the datasheet. I have voltage only in pins 1 and 7(3.1V). in other pins except gnd i have few mvolts.
i put some solder on each pin but nothing.

[Porto]

Re: lg 2234s no power at all

According to the datasheet the Vcc has to be 15v nominal, and 30v max.
Check all components between that pin and the rectified voltage on pin 1 of the rectifier, as Budm says, especially the caps. Not only measure the capacity but also the ESR if you are able to.

[budm]

Re: lg 2234s no power at all

Thanks, i've already found the datasheet. I have voltage only in pins 1 and 7(3.1V). in other pins except gnd i have few mvolts.
i put some solder on each pin but nothing.

There has to be DCV on pin 1 otherwise the SMPS will be in shut down due to BNO (brown out detection). You can have bad SMPS IC. You should also check the resistance between the VCC pin and Ground pin to see if it is really low and not allow the VCC to rise up to 16V (typ.) to run.
see the spec sheet again.
BNO
Brownout Protection Pin. Connected a resistor divider from this pin to bulk
capacitor voltage to set the brownout level and line compensation. When the
voltage of this pin is lower than threshold voltage, the PWM output will be off.

Brownout Turn-Off Trip Level min 1.05, typ. 1.10, Max 1.15 V.
Like I said, check or replace the startup cap and the rectifier in the secondary side or just buy a new board and save time troubleshooting.
You also do not have the main board connected while testing the output Voltage as I requested?

[vagos_89]

Re: lg 2234s no power at all

I tested the resistors and are all ok. I replaced the caps on primary(not smd) except the 150μF/450V because i didn't find the same, the rectifiers on the secondary and also the electrolytics there and i have the same measurements. i tested the optocoupler too.

If i have bad SMPS IC, the voltage on vcc not supposed to be right but to be bad the output voltage? If i understood correctly this voltage comes from optocoupler?

No i didnt had the mainboard connected when i measure. Nothing.
Already this board i bought fron ebay and comes to me faulty.

[budm]

Re: lg 2234s no power at all

If you look at the spec sheet of the SMPS IC, you will see that the VCC for running the CI is generated by the AUX winding of the transformer once the circuit is running, when power is first applied to the board pin 7 (VCC) gets the start up through the resistor.
Again: Please see the spec sheet of the IC as I suggested.
As I also indicated, the pin 1 BNO cannot be at 0V.
At this point you will be off getting good working board.